The present invention relates to an epoxy resin composition employed for encapsulation material of a semiconductor device and a semiconductor device using the same.
Recently as an encapsulation process for a semiconductor device, there has been mainly investigated an encapsulation process for a semiconductor by employing an epoxy resin composition, mainly comprising an epoxy resin, a curing agent and inorganic filler. Properties claimed for the encapsulation material have become severer year after year with increasing thermal resistance, reliability at a high temperature, reliability at high humidity and the like claimed for a semiconductor device. Among those, in order to improve crack resistance for moisture adsorption of the package, there has been developed and already employed practically encapsulation material comprising an epoxy resin having biphenyl structure having low moisture adsorption as an epoxy resin.
However, since the encapsulation material made from the epoxy resin having biphenyl structure generally has a glass transition temperature (Tg) of at most 130xc2x0 C., there was a problem of low reliability such as high temperature storage.
And as usual in order to maintain safety of the encapsulation material, the material contained a halogenated flame retardant such as a brominated epoxy resin as a flame retardant and an antimony compound such as antimony trioxide. But recently the environmental problems have become highly important, these compounds have been regarded as questionable even in ISO 14000. Therefore, a new flame retardant has been attempted to employ with environmental consideration. For example, there have been proposed an epoxy resin composition excellent in flame retardancy and reliability at a high temperature, which contains a phosphate compound, a red phosphorus flame retardant or the like without the halogenated flame retardant and the antimony compound as the conventional flame retardant. However, in case of employing the phosphate compound, there arises a problem of lowering reliability at high humidity due to apprehension of acid corrosion.
The present invention was made to solve the above mentioned problems. And the object of the present invention is to improve high temperature storage of an epoxy resin composition comprising an epoxy resin having biphenyl structure, and to provide a resin composition having high flame retardancy without a halogenated flame retardant and an antimony compound as a conventional flame retardant. Furthermore, the object is to provide a semiconductor device having high reliability obtained by employing the above mentioned epoxy resin composition as encapsulation material.
Namely, the present invention relates to an epoxy resin composition for semiconductor encapsulation comprising an epoxy resin, a curing agent, inorganic filler, a catalyst, a flame retardant, and an additive, wherein the composition is obtained by employing the epoxy resin mainly containing an epoxy resin having biphenyl structure, the phenolic resin mainly containing a zylok type phenolic resin (namely a phenolic aralkyl resin), a polysiloxane compound modified with polyether containing an amino group as the flame retardant, a polyimide resin as the additive, and not less than 87% by weight (usually 87 to 92% by weight) of the inorganic filler based on the total-composition.
And an amount of the polyimide resin as an additive is preferably 0.5 to 30 parts by weight based on total 100 parts by weight of the epoxy resin and the curing agent.
The polyimide resin as an additive is preferably the resin having both end groups thereof modified with an epoxy resin or a phenolic resin.
Further, the inorganic filler is preferably silica particle powder such as fused silica having a maximum particle diameter of not more than 75 xcexcm (an average particle diameter is usually 0.1 to 50 xcexcm).
The catalyst is preferably a phosphorus catalyst or a latent phosphorus catalyst.
A semiconductor device of the present invention is encapsulated by one of the above-mentioned epoxy resin compositions, wherein a semiconductor element is mounted on an iron frame, and loop length of a wire bond is not more than 3 mm.
And a semiconductor device of the present invention is encapsulated by one of the above-mentioned epoxy resin compositions, wherein a semiconductor element is mounted on a copper frame, and loop length of a wire bond is not less than 3 mm.
Table 1 shows composition of the epoxy resin composition in embodiment 1 of the present invention. The epoxy resin composition of the present embodiment comprises an epoxy resin, a curing agent, an inorganic filler, a catalyst, a flame retardant and an additive which is employed for semiconductor encapsulation material. The embodiment 1 of the present invention is explained below based on Table 1. xe2x80x9cPartsxe2x80x9d or xe2x80x9c%xe2x80x9d in Detailed Description respectively means xe2x80x9cparts by weightxe2x80x9d or xe2x80x9c%xe2x80x9d by weighty, unless otherwise specified.
The epoxy resin composition of the present embodiment is obtained by mainly employing an epoxy resin having biphenyl structure as an epoxy resin. But the epoxy resin having biphenyl structure as a main component may be mixed with an epoxy resin having terpene structure, a cresol novolak epoxy resin or an epoxy resin having naphthalene structure. In this case, 100 parts by weight of the epoxy resin having biphenyl structure as a main component can be mixed with 0 to 30 parts by weight of an epoxy resin having terpene structure, a cresol novolak epoxy resin or an epoxy resin having naphthalene structure.
As a curing agent, a phenolic aralkyl resin is mainly employed. But the phenolic aralkyl resin as a main component may be mixed with a phenolic resin having terpene structure, a phenolic novolak resin or a phenolic resin having naphthalene structure. In this case, 100 parts by weight of the phenolic aralkyl resin as a main component can be mixed with 0 to 30 parts by weight of a phenolic resin having terpene structure, a phenolic novolak resin or a phenolic resin having naphthalene structure. Mixing ratio of an epoxy resin and a curing agent is preferably 0.5 to 1.5 mole of a phenolic hydroxy group of the curing agent based on 1 mole of an epoxy group of the epoxy resin.
The chemical structures of these epoxy resins and these curing agents are respectively shown in the following Table 2 and Table 3.
In the present embodiment a polyimide resin is employed as an additive in order to raise a glass transition temperature of the epoxy resin composition and to achieve excellent high temperature storage. Examples thereof are poly(amide-bismaleimide), poly(pyromellitic imide), poly(ether imide), poly(amide-imide) and the like. A polyimide resin, of which both end groups are modified with an epoxy resin or a phenolic resin, may be employed. In these cases, 0.5 to 30 parts by weight of a polyimide resin is preferably mixed based on total 100 parts by weight of an epoxy resin and a curing agent.
As an inorganic filler, fused silica having maximum particle diameter of not more than 75 xcexcm is employed. But in case of a super small size package such as CSP type (chip scale package), fused silica having maximum particle diameter of not more than 50 xcexcm is preferably employed. The epoxy resin composition of the present embodiment contains not less than 87% by weight of the inorganic filler based on the total composition.
As a catalyst, a phosphorus catalyst and a latent phosphorus catalyst are employed. As the phosphorus catalyst, for instance, triphenylphosphine (hereinafter referred to as xe2x80x9cTPPxe2x80x9d) is employed. As the latent phosphorus catalyst, for instance, triphenylphosphonium-tetraphenylborate (hereinafter referred to as xe2x80x9cTPP-TPBxe2x80x9d), butyltriphenylphosphonium-tetraphenylborate (hereinafter referred to as xe2x80x9cBTPP-TPBxe2x80x9d), tetrabutylphosphonium-tetraphenylborate (hereinafter referred to as xe2x80x9cTBP-TPBxe2x80x9d) are employed. An amount of the catalyst is suitably 0.5 to 5 parts by weight based on total 100 parts by weight of an epoxy resin and a curing agent. There is no particular limitation for the catalyst employed in the present invention, as long as it promotes curing reaction between an epoxy resin and a curing agent.
In the present Embodiment, a polysiloxane compound modified with polyether containing an amino group is employed instead of a conventional halogenated flame retardant and an antimony compound. The polysiloxane compound modified with polyether containing an amino group is a highly stable silicone compound, which has been generally employed as glue and the like. The compound has high function as a flame retardant and is extremely excellent in electrical property, mechanical property, corrosion resistance and the like, if it is employed as a package. An amount thereof is suitably 0.2 to 5 parts by weight based on total 100 parts by weight of an epoxy resin and a curing agent. A chemical structure of a polysiloxane compound modified with polyether containing an amino group is shown in the following general formula (1). 
wherein R1 represents a methyl group, R2 represents a polyether group containing an amino group, a and b respectively represent a positive integer of 1 to 100 in the formula (1). Example of R2 is the following group. 
wherein a represents a positive integer of 20 to 100 and b represents a positive integer of 10 to 50 in the formula (2).
In the present embodiment except for the above-mentioned compounds there can be added epoxy silane as a coupling agent; a natural carnauba wax or a synthetic ester wax as a mold releasing agent; carbon black as a pigment; and the like.
A preparation method for an epoxy resin composition of the present embodiment is briefly explained below. In case of a liquid epoxy resin composition, the composition can be prepared by fully kneading the above-mentioned materials at 20 to 50xc2x0 C. employing a stirring mixing machine such as a mixer. On the other hand, in case of a powder epoxy resin composition, the composition can be prepared by fully kneading the above-mentioned materials employing a twin roll, a continuous kneading machine or the like after uniformly mixing employing a high speed mixing machine or the like. In this case, a mixing temperature is. preferably about 50 to 110xc2x0 C. After kneading, the desired epoxy resin composition can be obtained by thinly sheeting, cooling and crushing.
Table 4 shows physical property comparison between the encapsulation material comprising an epoxy resin composition of the present embodiment and the conventional encapsulation material comprising an epoxy resin having biphenyl structure.
High temperature storage as an encapsulation material is remarkably improved, since the glass transition temperature (Tg) of the present composition becomes not less than 150xc2x0 C. by employing (1) an epoxy resin having biphenyl structure mainly as an epoxy resin, (2) a phenolic aralkyl resin mainly as a curing agent, (3) 0.5 to 30 parts by weight of a polyimide resin as an additive based on total 100. parts by weight of the epoxy resin and the curing agent, (4) a polysiloxane compound modified with polyether containing an amino group as a flame retardant, (5) not less than 87% by weight of a fused silica as an inorganic filler based on the total composition.
And by employing a polysiloxane compound modified with polyether containing an amino group as a flame retardant without a halogenated flame retardant and an antimony compound as a conventional flame retardant, there is no harmful influence on environment and V-0 class can be accomplished according to UL94 as a flame retardant standard.
A semiconductor device obtained by employing the epoxy resin composition described in the above Embodiment 1 as encapsulation material is explained below.
For example, the above-mentioned epoxy resin composition can be employed as encapsulation material for a semiconductor device, wherein a semiconductor element is mounted on an iron frame, loop length of a wire bond is not more than 3 mm, and ball diameter is not more than 80 xcexcm. Examples of the device are memory packages such as SOJ type and TSOP type. In these cases loop length becomes short since LOC (lead on tip, wherein inner lead is located on a tip) structure is basic.
And the resin composition can be employed as encapsulation material for a semiconductor device, wherein a semiconductor element is mounted on a copper frame, loop length of a wire bond is not less than 3 mm, and ball diameter is not more than 80 xcexcm. Examples of the device are packages of micro computer or ASIC (QFP type). In these cases loop length is generally not less than 3mm, since they do not have an LOC structure.
These devices have not more than 5% of flow curvature of gold wire and they are excellent in moisture crack resistance, high temperature storage and flame retardancy.
The above-mentioned epoxy resin composition can be employed in a semiconductor device such as an PBGA type device compatible with multiple pinning and small sizing by arranging ball electrodes on the same face, a CSP type semiconductor device having super small size which has the same body size as a chip, or the like. All these semiconductor devices encapsulated by the above mentioned epoxy resin composition as an encapsulation material have package warp of not more than 50 xcexcm, and they are excellent in moisture crack resistance, high temperature storage and flame retardancy.
The epoxy resin composition described in above-mentioned Embodiment 1 can be employed as encapsulation material for various type semiconductor devices to provide a semiconductor device having extremely high reliability.